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Baking them for that long will evaporate a lot of water. This is a good thing. If they were in enough liquid to not dry out at all then they wouldn't brown and you would miss out on a lot of delicious flavor. That would be braising.

These may have been dryer than potatoes in the past if the potatoes were cut into smaller pieces (more surface area) or if the cook time was longer.

If you want your veggies to be more moist then you can cook them for a shorter length of time or toss them with some fat which will give the illusion of moisture as well as prevent some internal moisture from escaping.